Did you know your kidneys filter around half a cup of blood every minute? These bean-shaped organs in your lower back work hard to remove excess water and waste products from your blood, turning them into urine. When cancer begins in the kidneys, it can have a big impact on these important organs and the many body systems that depend on them.

The most common type of kidney cancer is renal cell carcinoma (RCC), which accounts for up to 85 percent of all cases. In RCC, tumors begin growing in a part of the kidney called the renal tubule. In this article, we’ll explain why the renal tubules are important, how they work, and what their role is in kidney cancer.

What Do the Kidneys Do?

The kidneys are important for maintaining the right balance of water, salts, and minerals — such as sodium, potassium, and calcium — in your blood. Much of this work is handled by about a million tiny filtering units called nephrons. Each nephron is made up of a filter called a glomerulus and a hollow tube called a renal tubule.

Each renal tubule runs alongside a blood vessel. As filtered fluid moves through the renal tubule, most of the water, minerals, and nutrients are reabsorbed by the blood vessel. Whatever remains continues through the renal tubules to become urine.

The kidneys are part of the urinary tract, which also includes:

• Two ureters — Tubes that carry urine from the kidneys to the bladder
• The bladder — A muscular organ that stores urine until it’s ready to be released
• The urethra — The tube through which urine leaves the body

How Do Renal Tubules Work?

The main jobs of the renal tubules are to return essential minerals and nutrients to the bloodstream and remove substances your body doesn’t need. To do this, renal tubules are divided into different sections, each with a specific function. Filtered liquid from the glomerulus passes through these sections, changing as it goes along. What’s left at the end becomes urine.

Here’s how each part of the renal tubule works:

• Proximal convoluted tubule (PCT) — This is where most of the water, minerals, salts, sugars, and nutrients are reabsorbed into the blood. The PCT is the first segment after the glomerulus.
• Loop of Henle — Next, this U-shaped section pulls more water and salts back into the blood. The loop of Henle also concentrates the remaining fluid by removing water.
• Distal convoluted tubule (DCT) — The DCT helps maintain a healthy acid-base balance by removing extra acid from the blood. This section fine-tunes the levels of minerals such as potassium and calcium.
• Collecting duct — This is the final stop before urine formation. Hormones adjust how much water and salt are removed to balance hydration and electrolyte levels.

Renal tubules also help your body get rid of certain medications by moving them from the blood into the urine.

How Does Cancer Develop in Renal Tubules?

Researchers believe that RCC begins in the cells lining the walls of the renal tubule. Different RCC subtypes may start in different parts of the tubule. For example, it’s thought that clear cell RCC originates in the PCT. Although there are more than 14 types of RCC, the most common are clear cell, papillary, and chromophobe RCC.

As RCC tumors grow, they begin to spread beyond the kidney. In stage 3 RCC, cancer cells have invaded nearby connective tissue, blood vessels, or lymph nodes. In stage 4 RCC, tumors may have reached distant parts of the body, such as the lungs and bones. This process is called metastasis.

Development of RCC Symptoms

In the early stages of RCC, most people don’t experience any symptoms. In fact, over half of new RCC cases are discovered during medical testing for unrelated health issues, often through imaging scans.

As a tumor grows in a renal tubule, it can damage this delicate structure. The cancer cells release molecules that trigger inflammation and cause surrounding cells to die. The nephrons around the kidney tumor begin to break down, and blood vessels in the area may rupture. When red blood cells leak into the urine and can’t be completely reabsorbed, it can result in bloody urine, which is a common symptom of RCC.

The growing tumor can cause pain and swelling in the lower back or sides — the area between the ribs and hips, also referred to as the flanks. Other common symptoms include:

• Unexplained weight loss
• Loss of appetite
• Fatigue (extreme tiredness that doesn’t improve with rest)
• Fever

Over time, the kidney tumor can affect how well the kidneys work. Larger and later-stage tumors have been linked to reduced kidney function.

Causes and Risk Factors

RCC makes up about 90 percent of cancers that start in the kidney. Like most cancers, RCC begins when damaged DNA causes cells to grow out of control.

Several factors can raise the risk of DNA damage in the kidneys and lead to RCC. These include:

• Smoking, which exposes kidney tissue to harmful chemicals
• Excess body weight, which disrupts the body’s hormone balance
• Hypertension (high blood pressure), which raises the likelihood of developing RCC

In addition, inherited conditions are responsible for about 4 percent of RCC cases.

What Happens if Renal Cell Cancer Is Found in the Tubules?

If you or a loved one is diagnosed with RCC, your healthcare team will perform tests to determine the cancer’s grade and stage. They’ll explain your treatment options, which may include surgery, such as partial nephrectomy (removal of part of the kidney) or radical nephrectomy (complete removal). Other options may be ablation (destroying the tumor with cold or heat), immunotherapy, or targeted therapy medications.

In general, the outlook for RCC is good. The five-year survival rate for all stages of RCC is 78 percent, according to the American Cancer Society. This means that people with RCC are, on average, 78 percent as likely as those without RCC to live at least five years after diagnosis. For people diagnosed in the early stages, which make up about two-thirds of cases, the five-year survival rate in the United States is 93 percent.

Early detection and the right care make a big difference in outcomes. If you notice symptoms or have risk factors for RCC, talk to your doctor about whether testing is right for you.

Talk With Others Who Understand

On MyKidneyCancerTeam, the social network for people with kidney cancer and their loved ones, members come together to ask questions, give advice, and share their stories with others who understand life with kidney cancer.

Have you or a loved one been diagnosed with kidney cancer? Does learning more about how the kidneys work help you better understand this condition? Share your experiences in the comments below, or start a conversation by posting to your Activities page.